1. Field of the Invention
This invention relates to an optical disc recording and/or reproducing apparatus comprising rotational driving means for an optical disc for rotating an optical disc at a constant linear velocity, tracking servo means for controlling the tracking of the optical disc on the recording track on the optical disc, and translating means for translating said optical pickup along the radius of the optical disc.
2. Description of the Related Art
In general, in an optical disc recording and/or reproducing apparatus, employing an optical disc as a recording medium, the recording track of the optical disc is scanned by a laser beam, as the disc is rotated at a constant linear velocity or at a constant angular velocity by disc rotating means, so that information signals are recorded or reproduced along the recording track. The optical head is moved along the radius of the disc by feed means for scanning the totality of the recording tracks on the disc. The optical pickup is controlled by focusing servo or tracking servo to permit the recording tracks on the optical disc to be scanned accurately by the laser beam.
The tracking servo controlling means for applying tracking servo to the optical head operates for producing a tracking error signal proportionate to the deflection in the track pitch direction of the recording tracks from the detection output of the optical pickup and feeding the tracking error signal feed back to the tracking actuator to perform a tracking control for coinciding the center of the spot of the laser beam with the center of the track. Among the methods known for detecting the tracking error in the optical disc recording and/or reproducing apparatus, there are a so-called three-beam method, as disclosed for example in U.S. Pat. No. 3,876,842 and a so-called pushpull method, as disclosed for example in U.S. Pat. No. 3,909,608.
With the optical disc apparatus for recording and/or reproducing the information signals by scanning the recording tracks with a laser beam, an optical head access control of translating the optical head to a desired track position is performed by a track jump control method, according to which, with the tracking control means remaining in operation, the optical pickup is shifted at a time by plural tracks, such as by 100 tracks, towards the desired target position. On the other hand, with an optical disc recording and/or reproducing apparatus in need of high speed accessing, the optical head is translated by translating means at an elevated velocity to close to the desired track position, with the tracking control means remaining standstill, after which the tracking servo control means is operated for accessing the target track position by track jump control.
With a so-called compact disc for audio or an optical video disc, the optical disc is rotated at a constant linear velocity along a recording track according to a constant linear velocity (CLV) system for rendering the recording density constant for the overall disc surface.
Meanwhile, certain optical disc recording and/or reproducing apparatus, such as an optical video disc, has a larger mass, and yet is in need of a high velocity rotation, such as 1,800 rpm. The mechanical system supporting the optical pickup of such apparatus is subject to considerable vibrations at a period corresponding to the period of rotation of the disc.
Among the transmission characteristics of tracking of the optical pickup is a resonance frequency of, as shown for example in FIG. 1.
In the optical disc recording and/or reproducing apparatus, employing the CLV system optical disc as a recording medium, it occurs frequently that the resonance frequency f.sub.0 of the optical pickup be included in the range of fluctuations of the rotational frequency of the optical disc rotated at a constant linear velocity by disc rotating means. With an optical recording and/or reproducing apparatus in which the resonance frequency f.sub.0 of the optical pickup is included in the range of fluctuations of the rotational frequency of the optical disc, if, with the tracking control means remaining standstill, the optical pickup is first translated at an elevated velocity to close to the target track position by optical pickup feed means, and tracking controlling means is subsequently operated for having access to the target track position by track jump control, the optical pickup unit may be vibrated with rotation of the optical disc in resonance with vibrations of a mechanical deck on which disc rotating means, optical pickup and translating means etc. are mounted, so that, if the tracking control means is actuated in such state of resonance, the tracking control means is driven into vibrations to render it impossible to operate the tracking servo control means in a regular manner. Object and Summary of the Invention
It is therefore an object of the present invention to provide an optical disc access control apparatus comprising disc rotating means for an optical disc for rotating an optical disc at a constant linear velocity, tracking servo means for controlling the optical disc in tracking the recording track on the optical disc and translating means for translating said optical pickup along the radius direction of the optical disc, wherein an accessing control may be performed so that the optical pickup may be moved stably and quickly to a target track position.
In accordance with the present invention, there is provided an optical disc recording and/or reproducing apparatus comprising disc rotating means for rotating an optical disc at a constant linear velocity, tracking servo control means for causing an optical pickup to track a recording track on said optical disc, translating means for translating the optical pickup along the radius of the optical disc, detection means for detecting if the rotational frequency of the optical disc is included within a frequency range in the vicinity of a resonance frequency of the optical pickup, and accessing control means for switching between a track jump control of translating the optical pickup to a target track position on the optical disc with the tracking controlling means in the energized state and a high speed accessing control of shifting the optical pickup by the translating means to the target track position on the optical disc with the tracking control servo means in the deenergized state for effecting accessing control of the optical pickup, wherein the operation of said accessing control means is switched depending on a detection output by said detection means so that the track jump control is effected when the rotational frequency of the optical disc is included in the frequency range in the vicinity of the resonance frequency of the optical pickup and high speed accessing control is effected by the translating means when the rotational frequency is outside of the frequency range in the vicinity of the resonance frequency of the optical pickup.
With the present optical disc recording and/or reproducing apparatus, it is detected by detection means whether or not the rotational frequency of the optical disc by the disc rotating means is included within the frequency range in the vicinity of the resonance frequency of the optical pickup and the operation of the accessing controlling means is switched depending on a detection output of the detection means, in such a manner that, if the rotational frequency of the optical disc is in the vicinity of the resonance frequency of the optical pickup, a track jump control is performed for translating the optical pickup to the desired track position on the optical disc, with the tracking control means remaining in operation, and that, if the rotational frequency of the optical disc is outside the range of frequency in the vicinity of the resonance frequency of the optical pickup, high-speed accessing control is performed by the translating means.